JPH01287628A - Second harmonic light generator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a method of generating second harmonic light.

2. Description of the Related Art In recent years, compact, high-output, short-wavelength light sources have been actively developed as light sources for optical disk devices. Especially the second
Shortening the wavelength using harmonic light has recently been attracting attention. Among them, a method using Cerenkov radiation has been put into practical use as a method for easily obtaining the second harmonic without requiring precise phase matching.

This is a waveguide that is formed by injecting protons in a stripe pattern onto the Lnibo3 single crystal surface.
Light in the m band is input, and light in the 4001 m band is emitted from the other side of the waveguide.

Problems to be Solved by the Invention However, since the conventional method uses LiNbO3, there is a limit to the conversion efficiency of the second harmonic, and therefore there is a limit to miniaturization. Moreover, LiNb0. Since it is an insulator, there is a problem when it is made into a monolink in order to integrate it with the semiconductor laser of the light source.

The present invention provides a second harmonic light generation method that allows a waveguide to be formed on a material constituting a semiconductor laser and provides high conversion efficiency.

Means for Solving the Problems In order to solve the above problems, the second harmonic light generation method of the present invention uses a compound semiconductor formed on a compound semiconductor substrate so that the mixed crystal ratio of each well layer gradually changes. Light with a wavelength corresponding to half of the lowest transition energy of the quantum well structure is incident on one side of the waveguide of the multi-quantum well structure, and light with a wavelength corresponding to the lowest transition energy of the quantum well structure is input from the other side of the waveguide. It consists of obtaining.

Effect: With the above configuration, the waveguide has a quantum well structure with spatially inclined potentials, so second harmonic light with high conversion efficiency can be obtained by Cerenkov radiation.

Embodiment In the present invention, by tilting the band gap in the well layer of a quantum well structure as shown in FIG.
The votents are made spatially non-inversion symmetric to obtain a second-order electro-optic effect.

By the way, when a second harmonic is generated using a quantum well structure, if the energy of the generated second harmonic is equal to or higher than the lowest transition energy of the quantum well, it will be absorbed and cannot be extracted.

Therefore, the material constituting the quantum well structure must have a large band gap so that the energy of the second harmonic is below the lowest transition energy of the quantum well structure, and in the example, it has a band gap in the 400 nm band. A quantum well structure made of ZnS and ZSSa was used as the material.

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of a waveguide in a specific embodiment of the present invention. In FIG. 1, 1 is n-GaAs (carrier density N~1017d, thickness a=sooμm), 2 is Z
n5 (N~10167, d=1 μm), 3 is Z
A layer of n5zS,z (100 people) /Zn5 (100 people) is formed by increasing the mixed crystal ratio X of S/815 in the well layer from Q to 0.5 in the crystal growth direction, as shown in Figure 2. By doing so, the band gap is gradually widened and a spatially non-inversion symmetrical structure is obtained, resulting in a multi-quantum well structure with 60 cycles. 4 is striped 5i02
A waveguide is formed in conjunction with the multiple quantum well layer. The waveguide length is 6M and the width is 2μm. Note that ZnSSe and ZnS were grown using an MBK apparatus. In addition, anti-reflection coating was applied to both end faces of the waveguide after cleavage.

From one end of the waveguide having the above structure, a semiconductor laser beam of 880 nm, which corresponds to half the transition energy of the lowest level of the quantum well structure, is focused to ~1 μmφ so that the second harmonic is not absorbed. It was then incident. Then, from the other end of the waveguide, a second harmonic wave 44 that appears blue appears.
Light of 0 nm was emitted. This shows that the second harmonic is generated by the waveguide of this structure.

FIG. 3 shows the dependence of the output light intensity of the second harmonic on the incident light intensity when laser light with a wavelength of 880 nm is input into the waveguide. This result shows that the conversion efficiency from the fundamental wave to the second harmonic is proportional to the intensity of the incident light.

Figure 4 shows the dependence of the conversion efficiency on the incident wavelength, 880 n
Maximum conversion efficiency when light of m is incident? It has gained. From this, efficient conversion can be carried out by injecting light with energy such that the energy of the second harmonic is slightly lower than the transition energy of the lowest level of the quantum well structure. For light with a wavelength shorter than 880 nu, the second harmonic is absorbed by the well layer, resulting in a decrease in conversion efficiency.

From the above, semiconductor laser light of 880 nm to 100 m
It has been found that the second harmonic can be generated by making W light incident on a multi-quantum well waveguide as shown in FIG. In addition, in the 1° Naoike example, where the above-mentioned waveguide and semiconductor laser were integrated on the same G & M S substrate, similar results were obtained, and the well layer width was adjusted to 50 to 200 mm. ,
Similar effects were obtained when the S/Sθ molar ratio of Zn5zSθ+-x was 0 to 1 and the repetition period was 1 to 100.

Furthermore, a similar effect was obtained by approximating the potential shown in FIG. 2a by changing the bandgap stepwise as shown in FIG. 2 as a quantum well structure with a tilted potential structure.

Kokote showed ZnSSe/ZnS semiconductor materials in the 400 nm band, but ZnSS/ZnSn56 and G
Similar effects can be obtained with ΔmS/mdGaAs and the like.

Effects of the Invention As described above, the present invention can generate a second harmonic by employing a quantum well with a tilted potential in the well layer as a quantum well structure with a non-inversion symmetric potential. In addition, by using a quantum well structure, the well width and well shape can be changed.

Any nonlinear optical effect can be obtained by combining materials. Furthermore, semiconductor integration technology makes it possible to realize a highly functional waveguide that generates second harmonics. Its practical effect is that of a dog.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining one embodiment of the present invention, FIG. 2a is a diagram for explaining an example of a well layer of the quantum well structure of FIG. 1, and FIG. Diagram explaining an example, 3rd
The figure is a diagram explaining the dependence of the output light intensity on the incident light intensity in a waveguide according to an embodiment of the present invention, and FIG. 4 is a diagram explaining the dependence of the conversion efficiency on the incident light wavelength in a waveguide according to an embodiment of the present invention. This is a diagram. 1...NC&MUS substrate, 2...Zn
3,3...Zn5xSj-zC100 people)/Z
n5 (100 people) x 60 multiple quantum well structure, 4...
...5in2 stripes. Name of agent: Patent attorney Toshio Nakao, and one other person

Claims (1)

[Claims] From one end of the waveguide, which has a quantum well structure in which semiconductor materials with different bandgaps are stacked alternately and the spatial potential of the well layer is inclined in the thickness direction, the lowest level of the quantum well structure is A method for generating second harmonic light, comprising inputting light having a wavelength corresponding to half of the energy, and emitting a second harmonic of the incident light from the other end of the waveguide.